A typical pair of running shoes lasts somewhere around 300-500 miles. (You could probably stretch a pair further than that, but you run much higher risk of injury once the cushioning wears down.)
If you put in a modest 5 miles a day and have two pairs in rotation, then expect to replace both pairs every 6 months (if not more often). It is not uncommon for semi-serious runners to spend $100+ on each pair of shoes. From that perspective, $500/year doesn't seem that outrageous.